Various types of vaporizing apparatus have been known for treating air. Watkins, U.S. Pat. No. 3,923,934, issued Dec. 2, 1975, shows a device for vaporizing a liquid into the air to control odors. Such a device is more broadly applicable to the dispensing of liquids, including odorants, deodorants, and air fresheners.
The Watkins device uses a vaporizing element, which is described in further detail in Watkins, U.S. Pat. No. 3,885,737, issued May 27, 1975.
In prior devices of this type, replacement of the vaporizing element was based on observation by the user, either of the time of usage, or the effectiveness of the vaporizing cartridge. It would be advantageous to assist customers in determining when to replace, not only the vaporizing element, but also any other replaceable elements, such as air filters, in such units.